How to put my pc on the lan?

we have a home lan with win10 machines on it.
i have a laptop, lenovo thinkpad, on the same lan: uses the same router.
in windows explorer the laptop can see the other computers and their shares.
from another computer I can see the laptop in windows explorer but I don't see its shares.
the win10 system shows me a login screen for the laptop.
i input the username and password and it tells me they're wrong. will not log me in.
I use the username I think I have and that 'whoami' on cmd on the laptop says I am.
I use the login - a four digit number - that i always use on the laptop.
how to troubleshoot this issue?
p.s. the laptop can see the win10 pc and can log in to it.
it's just I can't do it from the win10 end.

Are you entering the credentials of the computer you are accessing remotely?

Have you actually shared any folders on that specific machine? Is the machine on the same Workgroup? Are they all set to Private Network? Is Network Discovery turned on?